Cyst wall formation and endogenous carbohydrate utilization during synchronous encystment of Phytophthora palmivora zoospores

Summary Vigorous agitation caused the zoospores of Phytophthora palmivora to undergo rapid synchronous encystment. The rate of encystment was determined by counting the number of cells with an alkali-resistant cyst wall. 50% of the zoospores formed an alkali-resistant cyst wall within 60 sec of agitation; after 120 sec, essentially all zoospores had encysted. The rate of spontaneous encystment in nonagitated suspensions was much slower. The flagella of nearly all zoospores disappeared within 30 sec of agitation, i.e. prior to the formation of an alkali-resistant cyst wall. Zoospores depend on internal reserves for synthesizing their cyst walls. Approximately 70% of the total carbohydrate in motile zoospores was extracted with water after treating the cells with 70% éthnol. During synchronous encystment, this carbohydrate fraction composed largely of glucans decreased markedly while the insoluble carbohydrate fraction (cyst wall glucan) increased correspondingly. Clearly, the conversion of cytoplasmic glucan into wall glucan plays a major role in zoospore encystment.